Specialty crop growers throughout the country will benefit from a new $3.7 million USDA grant won by NC State to find sustainable control options for the invasive brown marmorated stink bug (BMSB).
Now that BMSB is detected in 43 states and is adapting to new climates, more needs to be done to manage the pest from a national perspective, says NC State Extension Entomologist Jim Walgenbach, principle investigator in the project. The grant is sponsored by USDA National Institute of Food and Agriculture (NIFA) Specialty Crops Research Initiative Program, and includes the cooperation of scientists from 16 land grant universities across the country as well as the USDA-ARS.
BMSB garnered attention in 2010 after it decimated many crops in the mid-Atlantic, most notably apples and peaches. The pest had become well-established in the mid-Atlantic after it was discovered in Pennsylvania in 2001 and was well-known for being an urban nuisance and a pest of fruits and vegetables. The value of crops most susceptible to BMSB—namely tree fruits, vegetables, nuts and grapes—is estimated to be over $23 billion.
In response to the 2010 infestation, Tracy Leskey of USDA Agricultural Research Service and George Hamilton of Rutgers University invited entomologists and other experts in the mid-Atlantic region to form a new working group, funded by the Northeastern IPM Center. The working group also included experts from regions where the pest was present but not yet a problem.
“It was the first time we had a collection of land-grant scientists, ARS scientists, farmers, business owners and others to deal with this pest,” said Leskey.
For several years, growers south of Virginia seemed to have little to worry about; most sightings of the pest didn’t coincide with crop losses. After 2011 that seemed to change, and in recent years growers as far south as Georgia and Alabama began reporting the pest as an agricultural and urban pest. This past year, several entomologists from the South formed their own BMSB working group to track the pest in the southern states and assess its habitat in southern crops.
In 2011 members of the mid-Atlantic working group, along with others concerned about the pest’s spread, collaborated on a USDA NIFA specialty crop grant to study the pest’s biology in that region and develop short-term mitigation strategies to prevent severe crop losses. The research resulted in the identification and recommendation of several types of insecticides to control the pest.
While the chemical tools helped “stop the bleeding,” Walgenbach says the sole reliance on insecticides is not sustainable for the long term. Most of the insecticides being used are broad-spectrum pyrethroids and neonicotinoids, which have eliminated natural enemies of other pests that growers don’t typically have to worry about.
The problem is most apparent in apples, where predators and parasites play an important role in biological control of several important secondary pests. The consequences of spraying for BMSB has led to increased problems with mites, woolly apple aphid and San Jose scale.
Some tree-fruit growers increased their post-bloom sprays from 5 to 15 applications per year after BMSB appeared. Experts are concerned that if the current spray schedule continues, growers could be facing insecticide-resistant stink bugs.
The recent USDA NIFA grant will seek out natural enemies that can keep the BMSB within threshold population levels that won’t cause significant economic damage.
The first step of the project is to survey predators and parasitoids of BMSB on a national scale in both agricultural and non-managed habitats. Walgenbach says that in the pest’s native habitat of Asia, parasitoids tend to have a far greater impact on BMSB than the parasitoids native to the U.S. Surveys to date suggest that native parasitoids in cropping systems do not play an important role in controlling BMSB populations. However, scientists have noticed a difference in wooded areas.
“We have found that parasitoids residing in arboreal habitats seem to be more efficient in parasitizing BMSB eggs,” says Walgenbach. “Increasing biological control in that area could have a major impact on population suppression, because that’s where a large portion of BMSB populations reside in the spring and fall.”
Parasitoid insects insert their eggs inside the body or egg of another insect species. When the eggs hatch, the host species dies, and the larvae feed on it.
Surveys for natural enemies in the pest’s native range of China, Japan and South Korea revealed the stink bug egg parasitoid Trissolcus japonicus. T. japonicus typically parasitizes 65 to 90 percent of BMSB eggs in Asia. The parasitoid was discovered in conjunction with the previous BMSB specialty crops project.
“The parasitoid was definitely a game changer,” Leskey said.
Kim Hoelmer, a research entomologist with the Beneficial Insects Introduction Research Unit with USDA Agricultural Research Service has been researching the parasitoid in quarantine. Before the parasitoid can be released, scientists must prove that it will not severely damage native predatory stink bugs. For T. japonicus, that means determining the probable impact in the wild.
“In the wild, an egg-producing female is capable of assessing the quality of a host and can decide whether it’s a good species or not to lay its eggs into,” says Hoelmer. “If it’s not, the parasitoid will leave it alone.”
Testing in lab quarantine has shown that T. japonicus females will lay their eggs inside some native stink bug species that they are confined with—including some of the beneficial native stink bugs—if they have no other choice. In tests where they are free to choose a host, however, they prefer brown marmorated stink bugs.
While completing the laboratory trials, Hoelmer has begun the process of petitioning the USDA Animal and Plant Health Inspection Service to grant formal permission to release T. japonicus for BMSB control.
Fortuitously, several “adventive” populations of T. japonicus that are genetically distinct from the lab specimens appeared in four states, namely Maryland, Virginia, the District of Columbia and Washington State.
“One of our tasks is to monitor those field populations,” says Hoelmer. “If they spread quickly, we may not need to release our quarantine populations. We may learn from the populations already in the field that they do not attack other stink bugs.”
To date parasitoid eggs have been recovered only from BMSB eggs in arboreal habitats in the wild. Leskey, who will be studying the biological and chemical ecology of BMSB, says that the parasitoid seems to be spreading and establishing itself fairly well.
“Finding the adventive populations puts us in a good position since we have to find a way to control this pest,” Hoelmer says.
While experts are not expecting to be able to totally eliminate chemical control, they are trying to find ways to reduce insecticide use by reducing both the number of insecticide sprays and area of fields sprayed. Enhancing the level of biological control will be an important contribution, but additional methods will be developed. These involve habitat manipulation strategies such as using trap crops to attract the pest away from the cash crop, and behavioral control such as using the insect’s pheromone in attract and kill techniques. Also, BMSB damage is often most severe on the periphery opposed to center of fields, so limiting insecticide sprays to specially defined areas can also reduce pesticide inputs.
In the past few years, scientists have discovered other hosts frequented by BMSB in the absence of fruit and vegetable crops. A collection of other hardwood trees, including tree of heaven, cherry, walnut, and paulownia, along with field crops including corn, cotton ad soybean harbor BMSB populations. Scientists are currently studying how BMSB transitions between these harborages and their preferred fruit and vegetable crops during the season.
“This project will provide needed information on its ecology and effectiveness of classical biological control of BMSB – i.e., importation of natural enemies from the homeland of an invasive pest to established populations in new areas of invasion,” Walgenbach says. “It’s not yet clear whether these adventive populations of T. japonicus can be transferred to different areas in the U.S., but I’m hopeful that we can so as to accelerate the establishment of this important natural enemy.”